皖赣相邻地区双桥山群沉积序列及沉积环境分析

Sedimentary Sequence and Environment of Shuangqiaoshan Group from the Adjacent Area Between Anhui and Jiangxi

皖赣相邻地区位于江南造山带东段北缘,双桥山群为区内广泛分布的一套厚度巨大低绿片岩相变质的以泥砂质细碎屑岩为主含少量火山岩的复理石建造。综合岩石组合及沉积构造分析,其可能为一套形成于大陆边缘岛弧构造背景下的陆棚斜坡-滨浅海相火山-陆缘碎屑岩建造组合体,具体可划分出次深海-陆棚边缘斜坡相、浅海陆棚相、陆棚斜坡相、陆棚斜坡相-陆棚相4个阶段的沉积相,显示该时期海盆演化已处于萎缩闭合阶段。横涌组和安乐林组中近源间断不完整"鲍马序列",主要为浊流和部分砂质碎屑流成因,分别形成于古华南洋新元古代陆缘俯冲作用下有限俯冲过程中和俯冲之后洋盆狭缩海退环境;从火山作用随沉积作用协同演化角度对沉积作用与大地构造的关系分析来看,源于洋壳俯冲作用的火山活动可能始于研究区南西。研究结果从沉积地层学角度,为新元古代皖赣相邻地区大地构造演化提供了重要证据。

The adjacent area between Anhui and Jiangxi is located in the northern margin of the eastern section of Jiangnan orogenic belt,in which Shuangqiaoshan Group is widely distributed in a large-thickness and lowgrade greenschist-facies metamorphic flysch formation which is given priority to with argillaceous-arenaceous metamorphosed fine clastic rocks and contains a small amount of volcanic rocks. Synthesizing analysis of rock assemblages and sedimentary structures shows that Shuangqiaoshan Group may be formed in a set of volcanicterrigenous clastic rocks which can be divided into four stages of sedimentary facies about the bathyal-shelf margin slope,neritic shelf,shelf slope and shelf slope-shelf facies under tectonic background of continental margin island arc,indicating the shrinking-closing stage of the basin evolution during the period. The proximal source region and discontinuous incomplete Bouma sequence of Hengyong Formation and Anlelin Formation,mainly generated by turbidity current and few by sandy debris flow,respectively formed during the northward limited subduction process of the lithospheric fault block in South China with oceanic crustal sea areas,and after that under ocean-basin thinning regressive environment in Neoproterozoic. From the perspective of volcanism with sedimentation co-evolution on the relationship between the sedimentation and tectonic analysis,the volcanic activity resulted from oceanic crust subduction may be started from southwest of the study area. This study provides the important evidence for the geotectonic evolution of the Neoproterozoic in the adjacent area betweenAnhui and Jiangxi from the aspect of the sedimentary stratigraphy.